The production of long, substantially defect-free carbon nanotubes (CNTs) may be necessary to make usable materials that can retain the desirable properties of individual nanotubes. In general, nanotube growth may be limited by various growth conditions, including (1) fuel starvation, (2) catalyst size and stability, (3) carbon diffusion rates on the catalyst surfaces, (4) nature of the reaction gas, (5) duration within the reaction zone, and (6) temperature of the reaction zone.
It has been observed that nanotube growth seems to be non-linear with residence time within a reactor. In addition, it has been observed that larger catalysts tend to exhibit substantially no growth. To that end, termination of growth may be correlated to the change in the catalyst particle size during nanotube growth.
Optimization of growth parameters, including those indicated above, has recently led to a measurable increase in carbon nanotube production and strength of material made from these nanotubes. One primary parameter which appears to be related to strength is length of the nanotube. For example, long samples of yarns (i.e., intertwined or spun carbon nanotubes), some over about 10 meters in length, with a strength of over about 1.4 GPa have been produced. However, even at such length, there may still be about 5 to about 10 times less than the potential material strength of a yarn, when based on individual tube strength estimated at about 30 GPa. Creating longer individual nanotubes should translate into material strengths that more closely approach the average strength of individual nanotubes.
Accordingly, it would be desirable to provide a system and method capable of controlling specific parameters necessary for optimizing growth, as well as enhancing the strength of materials made from the nanotubes being produced.